The present invention relates to the field of carpet securements commonly referred to as "carpet strips," and further relates to methods of manufacture useful in making carpet strips and other extruded polymeric articles.
Carpeting is commonly installed in buildings using securements known as carpet strips. Each such securement includes an elongated striplike body and many tacks protruding upwardly through the body so that the shanks and points of the tacks extend upwardly from the strip, the heads of the tacks being disposed on the underside of the strip. Nails are prepositioned in the strip by driving them partially through the body from the top surface. In the installation process, the strips are nailed to the floor using these prepositioned nails so that the top surface of the strip faces up, and the shanks and points of the tacks are exposed. When the carpet is forced down onto the top surface of the strip, the points of the tacks engage the carpet backing and hold the carpet in place.
The bodies of carpet strips traditionally have been made of plywood. However, plywood is expensive and it tends to splinter when the tacks and nails are driven. Various proposals have been advanced to replace the wooden bodies of carpet strips with polymeric bodies. Simple direct replacement of wood with a polymer, retaining the same rectangular shape and size used for the wooden strip, ordinarily is impractical both for economic reasons and for technical reasons. The cost of the polymer required to make such a strip typically exceeds the cost of wood even if low cost, recycled polymers are used. If the tacks or other fasteners are driven to full depth, so that the head of each fastener is recessed into the bottom surface of the strip, the polymer can crack. If the polymer does not crack, it may be difficult to drive the fastener all the way in so as to recess the head.
Frebraro, U.S. Pat. No. 3,673,633 discloses various forms of carpet strips, including solid strips and also including strips combining a fluted or grooved polymeric body with a metallic striplike insert. The metallic insert has prongs replacing conventional tacks, so that no tacks are driven through the body. Sutton et al. U.S. Pat. No. 3,828,391 discloses a molded polymeric strip with integrally formed sharp projections for engaging the carpet, as does Nedel U.S. Pat. No. 3,858,269. Anderson et al., U.S. Pat. No. 4,970,754 discloses a carpet strip body in the form of a substantially solid billet of foamed polyurethane. Perhaps because of the costs difficulties associated with producing relatively complex articles as described in these patents, none of these approaches has been widely adopted. Thus, there has been a substantial, unmet need heretofore for improvements in the design of carpet fasteners to facilitate practical application of polymeric bodies in carpet strips.
Additionally, there have been needs for improved methods of polymer processing for forming the polymeric bodies of carpet strips, and for forming other polymeric articles. Elongated polymeric articles commonly are formed by extrusion. In the extrusion process, the polymer, while in a soft condition at a temperature above its melting point and/or glass transition temperature, is forced through an extrusion die. The extruded polymer or "extrudate" is pulled in a downstream direction away from the die and cooled. Where the extrudate includes a gas, the extrudate may be passed through at least one sizing die. For example, the extrudate may be passed through a sizing die chamber having upstream and downstream dies. The downstream die has lips with contact surfaces defining an opening corresponding to the desired size and shape of the article. A subatmospheric pressure is maintained within the sizing die chamber. Under the influence of the subatmospheric pressure within the sizing die assembly chamber, the gas in the extrudate tends to expand, thereby forcing the extrudate into contact with the contact surfaces of the sizing dies. Such a sizing die assembly can assist in maintaining accurate control of the size and shape of the finished product. Unfortunately, use of such a sizing die assembly materially reduces the speed with which the extrudate can be pulled from the extrusion die and thus materially increases the cost of the extrusion process. This renders it considerably less practical for use in production of high volume, relatively low cost items such as carpet strip bodies. There is accordingly an acute need for a solution to this problem as well.